Piezo materials can be used both as sensors and as actuators. When mechanical stress is applied to a piezo material, an electric charge is produced. Conversely, piezo materials may respond with mechanical motion when subjected to electrical signals. A piezoelectric element may be a block of ceramic material that may be described as a moving capacitor. As the piezoelectric element expands or contracts, its capacitance varies. These flexible properties of piezoelectric elements have made them popular in haptic applications.
Known ways of driving piezoelectric elements suffer from excessive power consumption or switching induced noise, or both. For example, driving a capacitive element with digital patterns may produce large surges in power because power is consumed only during transients and the impedance of the piezoelectric element can be very small on the rising and falling edges of a pulse, thereby resulting in substantial power consumption and switching induced noise. While the movement of some piezoelectric elements is based on inertia principles requiring fast edges, others require drive waveforms which are more sinusoidal in nature. In this resonant approach, a specific frequency of a sinusoidal waveform is applied to induce movement or deformation of the piezoelectric element. Although switching induced noise may not be a problem in the resonant approach, it suffers from substantial power consumption. The power consumption of the piezoelectric element is given in equation 1 below:
                    P        =                              1            2                    ⁢          C          ⁢                                          ⁢                      V            2                    ⁢          f                                    (                  Eq          .                                          ⁢          1                )            
Where:
P=Power Consumed,
C=Capacitance of the Piezoelectric Element,
V=Voltage Applied, and
F=Frequency of Drive Signal.
The circuit used to drive the piezoelectric element also may consume the same amount of power as the piezoelectric element. This is an inherent property of any driver used to drive a piezoelectric or capacitive element directly. Accordingly, the total power consumption is provided in equation 2 below:P=CV2f  (Eq. 2)
It is therefore a goal of an embodiment of the present invention to provide a device and method to drive piezoelectric elements in haptic applications that do not suffer from substantial power loss, have reduced acoustic and switching induced noise, and provide a more haptic rich environment.